A frog is used in a railway where two rails cross over each other, to provide support for the wheels as they pass over the intersection. A spring wing or spring rail frog has a movable wing rail that is connected only at one end, such that it moves laterally away from the frog to provide a flangeway when a wheel of a passing car engages the spring wing rail. Examples of basic spring wing frogs are described in U.S. Pat. Nos. 4,624,428 and 4,637,578, both to Frank.
A common problem with spring wing frogs is that if the spring wing closes quickly, as compared to the speed of the passing train, it may close after each wheel or between cars, and then be forced open again for the next wheel. In this case, the spring wing is subjected to a greater number of cycles in a given time frame, and is therefore susceptible to failure more rapidly. It is therefore preferable to provide a system in which the rate of closure can be controlled, so that a certain amount of time can be expected to elapse after each car wheel passes, before a spring wing is completely closed. In this manner, a spring wing may be expected to stay open until an entire train has passed, rather than constantly opening and closing as the train passes.
U.S. Pat. Nos. 6,158,697 and 5,806,810, both to Young et al., disclose latch holdback mechanisms (either physical or magnetic) designed to hold the spring wing in an open position for a given length of time. Hydraulic fluid is pumped through the system to engage the latch mechanism and hold the spring wing open each time car wheels pass, and bleeds off gradually to release the latch once the wheels have ceased passing. U.S. Pat. No. 2,405,407 to Conley discloses a piston rod within an oil-filled cylinder and a spring connecting the piston and the cylinder. The movement of the piston rod upon opening the spring wing compresses the spring. Movement of the piston further opens a valve on the piston, allowing oil to pass through the valves and hold the piston in an open position. A slow oil leak through a small hole in the valve allows gradual pressure equalization within the cylinder so that the piston and spring wing return to the closed position some time after the last car wheel has passed. PCT Publication No. WO 01/85524 to Moscato et al. discloses a more complex system having three fluid chambers and four fluid flow regulators, in which a hydraulic timing device or similar controller uses a restrictor valve to move the controller at a linearly varying rate depending on the position of the spring wing rail. That is, when the rail is open, the rate of closure is relatively slow, which prevents the rail from closing before the next set of car wheels passes. To avoid excessively slow closure, a relief port is provided, which circumvents the restrictor valve and allows the spring wing to close at a faster rate once it nears its home position. A high pressure relief valve is also provided to protect the timing device from excessively high pressures within the chambers.
However, a further consideration is that once the spring wing is released by the passing car wheel, it is biased to return to its original position and can do so very quickly, slamming against the side of the frog and causing noise and damage or wear to the spring wing and the frog. It is therefore preferable to provide a system that retards the movement of the spring wing, so that it closes more gently against the side of the frog, minimizing the chances that the frog or spring wing will be damaged by the impact. U.S. Pat. No. 2,036,198 to Cooper discloses a dash pot arrangement to automatically control the spring wing movement and allow it to return to a closed position in a gentler manner.
Hydraulic cylinders have been seen as a good way to deal with both controlling the speed and timing of the spring wing closure. In most systems, the piston rod is connected to the spring wing and moves the piston in the cylinder as the spring wing opens, which causes a pressure change within the cylinder. Similar to Conley, U.S. Pat. No. 1,689,841 to Powell provides a by-pass groove in the cylinder wall to allow graduated oil flow during the piston stroke, to control the movement of switch points. In U.S. Pat. No. 2,686,668 to Bettison, a sliding valve is free to move a short distance along the piston rod between the piston head and a shoulder on the piston rod. Movement of the valve covers and uncovers openings in the piston head, such that oil flows to the correct side of the cylinder to control movement of the piston rod and spring wing. Other earlier systems use a similar mechanism, wherein the pressure change causes a check valve to open, which allows fluid to transit from the pressurized side of the piston to the slightly lower pressure rod side of the piston. The volume of the fluid transiting the piston requires more space than the space created by the piston movement and a compressible gas, typically nitrogen, is provided in cylinder to compensate for the difference in volume between the two sides of the cylinder for a given movement of the piston. Once the piston is fully displaced and starts to return to its original position, the pressurization reverses and the fluid on the rod side of the piston increases, closing the check valve. The hydraulic fluid is then slowly bled from the rod side to the non-rod side of the cylinder, for example with a metering jet or other orifice, allowing the spring wing to close in a controlled manner.
However, hydraulic cylinders are susceptible to several potential problems. Any small openings through which fluid is expected to pass may be subject to erosion and plugging due to contaminants in the fluid. Components such as the metering jet are not replaceable, and may fail. Further, such components, or any grooves or other orifices within the hydraulic cylinder, are not adjustable, so the closure speed and timing cannot be changed, for example for different train speed limits mandated by different locations.
Another potential drawback is hydraulic fluid leakage—if the fluid within the cylinder leaks, the cylinder will eventually have insufficient fluid and will not operate properly. The hydraulic retarder disclosed in U.S. Pat. No. 2,686,668 to Bettison includes a pathway between an oil reservoir and the likeliest area of the cylinder to leak, such that any leakage is pulled back into the reservoir and can be returned to the cylinder.
Even if there is sufficient fluid within the cylinder, hydraulic cylinders may still be susceptible to hydrolocking. The piston will always try to travel its full stroke through a cylinder, but if the spring wing moves very quickly, it forces the piston rod to likewise move very quickly. If the hydraulic fluid is unable to transit quickly enough through the check valve or any other openings, which tend to be relatively small and restrictive, the non-rod side of the cylinder will be too full of incompressible fluid, which prevents the rod from travelling far enough and causes it to buckle. The resulting piston rod distortion results in misalignment of the check valves and causes a functional failure, if not a complete structural failure.
It is therefore an object of this invention to provide a mechanism to control the movement of the spring wing on a frog that overcomes some or all of the foregoing difficulties.
It is a further object of the invention to provide a spring wing controller that can respond quickly to the movement of the spring wing, with reduced chance of failure due to the rapid movement of the spring wing.
It is a further object of the invention to provide a control mechanism for a spring wing that is adjustable for various operating conditions.
These and other objects of the invention will be better understood by reference to the detailed description of the preferred embodiment which follows. Note that the objects referred to above are statements of what motivated the invention rather than promises. Not all of the objects are necessarily met by all embodiments of the invention described below or by the invention defined by each of the claims.